To characterize functional interactions between vertebrate L1-type molecules and other membrane and receptor proteins, I will express vertebrate L1-type molecules in Drosophila S2 cells to address the following specific aims: A) Determination whether the adhesion-dependent activation of membrane skeleton recruitment is a conserved feature of other vertebrate L1-type molecules. I will express a number of different vertebrate L1-type molecules (e.g. chicken Nr-CAM, Ng-CAM and neurofascin) in Drosophila S2 cells and test whether they induce homo- or heterophilic cell aggregation and whether they are able to recruit the membrane skeleton molecule ankyrin to cell contact sites. B) Demonstration of a functional cis-interactions between L1-type molecules and other neuronal membrane proteins. Different L1-type proteins and suspected L1 ligands, such as F11, axonin-1 or FGF-receptors, will be expressed in S2 cells. I will test for cis- and/or trans-interactions between these molecules by cell aggregation experiment and L1-dependent functional changes, such as changes in FGF-receptor autophosphorylation and the recruitment of the membrane skeleton to cell contact sites. C) Identification and characterization of novel ligands interacting with L1-type cytoplasmic domains. I will attempt to clone a Drosophila homologue of a new PDZ-domain protein which has been identified in Dr. Rathjen's lab as a ligand of the neurofascin cytoplasmic domain. The neuron-specific splice form of Drosophila neuroglian has a PDZ recognition motif at its COOH terminus and I will test whether it interacts with the novel PDZ-domain molecule by by yeast two-hybrid analysis and by co-expressing both molecules in S2 cells.